Saturday's M.A.C cosmetics Oscar Luncheon for Mo'Nique at Phillippe Chow in L.A. was already the place to be on Saturday - with such legends as Ruby Dee on hand to honor the "Precious" actress.

But then "Precious" producer Oprah Winfrey made an surprise appearance and took the party to another level.

Mo'nique and Oprah Winfrey

Attendees like Shondrella Avery and Jackee Harry "flipped out" and even "had tears in their eyes," according to the New York Daily News' Gatecrasher column. "The ladies really couldn't believe she was at the same party," the source said.

"But ever the diva, Mo stole back the limelight when she insisted the entire Parisian-themed luncheon area be turned into a dance floor when the guests finished eating," Gatecrasher reported. "She then requested that Marvin Gaye's "What's Going On" be turned on full blast."

A witness said: "Mo'Nique started a conga line that went throughout the restaurant and eventually led out to the valet parking area. The ladies, who were all decked in pearls and white gloves, were really getting down."

John Demsey, the chairman of the M.A.C AIDS Fund + President of Estee Lauder companies, announced a grant to Women Alive for $25,000 in Mo'Nique's name.